The operating principle of an inkjet printing device is that some ink droplets with fixed size are sprayed onto a surface of a printing stock. The disadvantage is that it needs some time to dry the liquid ink. If the amount of the droplets sprayed on a paper is too large and the paper cannot fix or absorb the droplets rapidly, it will cause the ink droplet to flow, diffuse or permeate on the paper. This makes the printed image look dirty, fuzzy, and with a decreased contrast, or even makes the paper distorted. The current inkjet printing device is turned from the beginning of 4 color into 6, 7, 8 or even more color, and the size of the ink droplet can also be divided into big, medium and small. When several different kinds of ink are printed in a same place simultaneously, it can easily lead to a droplet accumulation to cause ink pilling and flowing etc.
There are some different methods to solve the ink pilling problem, for example, to add a coating on the surface of the paper in order to facilitate the ink droplet absorbing and fixing. In addition, the ink properties can be changed, i.e. to use “quick-drying” ink. However, the improvement of paper and ink performance is limited, it cannot solve the problem of ink pilling completely and may even create new problems to cause the image quality decreasing. On condition of particular paper and ink, the most effective way to solve the problem of ink pilling is to control the ink amount printed on the paper, and this needs to determine a threshold of the output amount of the ink that can just avoid the ink pilling, that is, to determine the total amount of ink.
The most commonly used method for determining the total amount of ink includes: printing an evaluating graph; and then determining an appropriate total amount of ink according to certain rules by an operator. But the method has a problem that the determined result is highly affected by subjective factors. Because each person's sense to the color is different, for the same evaluating graph, to observe the total amount of ink by different people will usually obtain different results. Therefore, the operator needs to have some experience to determine a correct total amount of ink.